MySQL 5.5常用信息函数有什么
发布时间：2021-12-25 01:46:20 所属栏目：MySql教程 来源：互联网
导读：这篇文章主要介绍了MySQL 5.5常用信息函数有哪些，具有一定借鉴价值，感兴趣的朋友可以参考下，希望大家阅读完这篇文章之后大有收获，下面让小编带着大家一起了解一下。 CONNECTION_ID() 显示连接ID（线程ID） mysql SELECT CONNECTION_ID(); +--------------
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这篇文章主要介绍了MySQL 5.5常用信息函数有哪些，具有一定借鉴价值，感兴趣的朋友可以参考下，希望大家阅读完这篇文章之后大有收获，下面让小编带着大家一起了解一下。 CONNECTION_ID() 显示连接ID（线程ID） mysql> SELECT CONNECTION_ID(); +-----------------+ | CONNECTION_ID() | +-----------------+ | 50 | +-----------------+ 1 row in set (0.00 sec) CURRENT_USER() 显当前客户端连接的用户名和主机名 mysql> SELECT CURRENT_USER(); +------------------+ | CURRENT_USER() | +------------------+ | system@localhost | +------------------+ 1 row in set (0.00 sec) DATABASE() 显示当前连接的数据库名称 mysql> SELECT DATABASE(); +--------------------+ | DATABASE() | +--------------------+ | information_schema | +--------------------+ 1 row in set (0.00 sec) FOUND_ROWS() 显示SELECT语句的返回行数，忽略LIMIT语句，在存储过程里面很有用。 SQL_CALC_FOUND_ROWS告诉MySQL计算结果集中的行数，忽略LIMIT语句，行数可以通过SELECT FOUND_ROWS()来查询出 mysql> select * from dept; +--------+------------+----------+ | DEPTNO | DNAME | LOC | +--------+------------+----------+ | 10 | ACCOUNTING | NEW YORK | | 20 | RESEARCH | DALLAS | | 30 | SALES | CHICAGO | | 40 | OPERATIONS | BOSTON | +--------+------------+----------+ 4 rows in set (0.00 sec) mysql> SELECT SQL_CALC_FOUND_ROWS * FROM dept ORDER BY 1 limit 2; +--------+------------+----------+ | DEPTNO | DNAME | LOC | +--------+------------+----------+ | 10 | ACCOUNTING | NEW YORK | | 20 | RESEARCH | DALLAS | +--------+------------+----------+ 2 rows in set (0.00 sec) mysql> SELECT FOUND_ROWS(); +--------------+ | FOUND_ROWS() | +--------------+ | 4 | +--------------+ 1 row in set (0.00 sec) ROW_COUNT() 在MySQL 5.5.5版本之前，ROW_COUNT()返回上一条UPDATE, DELETE,或INSERT语句的行数，对于其他语句，这个返回值没有意义。 在MySQL 5.5.5版本，ROW_COUNT()返回下列值： DDL语句，例如CREATE TABLE 或 DROP TABLE：0。 DML语句，例如UPDATE, INSERT, 或 DELETE，ALTER TABLE 、 LOAD DATA INFILE和SELECT * FROM table_name INTO OUTFILE 'file_name'：实际影响的行。 SELECT语句:-1 SIGNAL 语句: 0 mysql> select * from t20; +------+ | id | +------+ | 200 | | 100 | +------+ 2 rows in set (0.28 sec) mysql> insert into t20 select * from t20; Query OK, 2 rows affected (0.20 sec) Records: 2 Duplicates: 0 Warnings: 0 mysql> SELECT ROW_COUNT(); +-------------+ | ROW_COUNT() | +-------------+ | 2 | +-------------+ 1 row in set (0.00 sec) SCHEMA() 显示连接的数据库名称 mysql> SELECT SCHEMA(); +----------+ | SCHEMA() | +----------+ | fire | +----------+ 1 row in set (0.00 sec) USER()、SESSION_USER()、SYSTEM_USER() 显当前客户端连接的用户名和主机名 mysql> SELECT SESSION_USER(); +------------------+ | SESSION_USER() | +------------------+ | system@localhost | +------------------+ 1 row in set (0.00 sec) mysql> SELECT SYSTEM_USER(); +------------------+ | SYSTEM_USER() | +------------------+ | system@localhost | +------------------+ 1 row in set (0.00 sec) mysql> SELECT USER(); +------------------+ | USER() | +------------------+ | system@localhost | +------------------+ 1 row in set (0.00 sec) VERSION() 显示数据库版本 mysql> SELECT VERSION(); +------------+ | VERSION() | +------------+ | 5.5.48-log | +------------+ 1 row in set (0.00 sec) LAST_INSERT_ID() 自增字段执行上一次的INSERT语句的值 mysql> create table test(id int auto_increment not null primary key, name varchar(15)); Query OK, 0 rows affected (0.08 sec) mysql> desc test; +-------+-------------+------+-----+---------+----------------+ | Field | Type | Null | Key | Default | Extra | +-------+-------------+------+-----+---------+----------------+ | id | int(11) | NO | PRI | NULL | auto_increment | | name | varchar(15) | YES | | NULL | | +-------+-------------+------+-----+---------+----------------+ 2 rows in set (0.00 sec) mysql> insert into test(name) values('Neo'); Query OK, 1 row affected (0.00 sec) mysql> insert into test(name) values('Lily'); Query OK, 1 row affected (0.00 sec) mysql> select * from test; +----+------+ | id | name | +----+------+ | 1 | Neo | | 2 | Lily | +----+------+ 2 rows in set (0.00 sec) mysql> select last_insert_id(); +------------------+ | last_insert_id() | +------------------+ | 2 | +------------------+ 1 row in set (0.00 sec) mysql> insert into test(name) values('Trinity'); Query OK, 1 row affected (0.00 sec) mysql> select last_insert_id(); +------------------+ | last_insert_id() | +------------------+ | 3 | +------------------+ 1 row in set (0.00 sec) 感谢你能够认真阅读完这篇文章，希望小编分享的“MySQL 5.5常用信息函数有哪些”这篇文章对大家有帮助。 （编辑：晋中站长网） 【声明】本站内容均来自网络，其相关言论仅代表作者个人观点，不代表本站立场。若无意侵犯到您的权利，请及时与联系站长删除相关内容! |
